Cases (e.g. cardboard boxes) are commonly sold in a folded flat (i.e. a knocked down) configuration. A case erector is a machine that assembles cases from the folded flat configuration into a three-dimensional form, typically having bottom box flaps taped or glued shut.
Known case erectors have two arms, typically configured with suction or vacuum cups, which grasp two adjacent sides of the box, respectively. Each arm then moves through 45 degrees thereby opening the box. In an application with a single arm, the single arm may move through 90 degrees. In either application, such arms are supported by bearing surfaces, which allow the pivotal rotation.
It is desirable to locate the fold between the two adjacent sides of the box that are grabbed by the two arms co-linearly with an axis about which the two arms pivot. This results in a design challenge, in that it is desirable to locate a (usually) vertical shaft (about which the arms pivot) in the same location that it is desirable to locate the fold in the box.
Two solutions are common. In a first solution, the fold in the box (between the two adjacent sides that are grasped by the arms) can be located “near” (but not exactly collinear with) the shaft about which the two arms pivot. This will cause the box to skew as it is opened. The skew occurs because the fold between the two adjacent sides of the box and the two arms do not pivot about the same virtual center point. This skew is generally unacceptable, and therefore a second solution is common.
In the second solution, the shaft about which the two arms pivot is located above (or below) the box, so that if the shaft were extended in one's imagination, the shaft would be co-linear with the fold between adjacent sides of the box. Since the shaft is located above the box as the box is moved into position to be opened, the arms must extend laterally outward from the shaft and also extend down to the box, so that vacuum cups carried by the arms may contact the adjacent sides of the box. This makes the overall device heavier and more complex, and requires arms having increased strength due to their length and other factors. While this solution allows the arms to be kept parallel to the box sides, (the arms reach down from above or up from below) the structure required to support the erecting arms must be more robust which will increase cost, complexity and overall size of the mechanism.